The invention relates to a pump with positive displacement for pumping and entrainment of a fluid in piping.
It extends to a device for thermal control of the components of a space system, such as an artificial satellite or a space station with a long service life.
Use of space systems with a long service life such as unmanned commercial satellites (for telecommunications, scientific or observation purposes etc.) or space stations, and in particular orbital stations, is tending to become considerably more frequent. As a consequence, the constraints of industrial production and cost are becoming increasingly important, as opposed to technical performance alone.
In particular, these space systems incorporate components, and in particular electronic components, which emit heat and have to be cooled, and dissipate increasingly high levels of power (with power densities which develop accordingly), and which must be kept within ever narrower temperature ranges. The distances of transport between the hot source and the cold source are also increasing. The conventional passive thermal control means (in particular by conduction or radiation) are thus insufficient.
When use of thermal conduction and radiation is insufficient, the known thermal control devices on board the satellites consist in general of heat pipes. In fact, heat pipes have the advantage of greater reliability and a longer service life than those of mechanical pumps. In fact, it should be noted that in a satellite, the service life of the equipment must be assured for several years, before launching takes place. Conventionally, this service life must be approximately ten to fifteen years.
However, heat pipes have disadvantages: in order to test them on the ground, they need to be placed on a low gradient which does not necessarily correspond to the configuration of flight, which detracts from the representativity of the tests; their dimensions need to be made to measure for integration in each space system; their rigidity is a constraint which causes problems during integration, which is sometimes difficult, or even impossible; they are very sensitive to the non-condensable gases which they produce, and their efficiency and characteristics are considerably affected by these non-condensable gases; and they have a low capacity for transporting thermal power.
In addition to heat pipes, thermal control devices have also been proposed which comprise one or a plurality of loops of heat-transfer fluid, associated with a pumping device of the capillary or mechanical type.
Pumping devices of a capillary type have a low transport capacity (limited flow rate and manometric height), in particular for tests on the ground in the presence of gravity; they are complex to start; and their tolerance for extreme operating modes is low (when the power to be transported becomes very low, or in the presence of non-condensable gases).
Mechanical pumping devices in the form of a centrifugal pump have been used in practice in certain manned missions (shuttles, capsules, stations etc) for operation of loops which use monophasic heat-transfer fluid.
In the very rare cases of unmanned missions where mechanical pumping has been selected, there has also been option for a centrifugal pump. Thus, the publication xe2x80x9cIntegrated Pump Assemblyxe2x80x94An Active Cooling System for Mars Pathfinder Thermal Controlxe2x80x9d Gajanana C. Birar et al, SAE TECHNICAL PAPER SERIES 961489 pp1-8, 26th International Conference on Environmental Systems, Monterey, Calif., Jul. 8-11, 1996, explains that use of a positive displacement pump was rejected, in favour of a centrifugal pump, for the thermal control loop of the Mars xe2x80x9cPathfinderxe2x80x9d probe. This probe was qualified for a service life of a few months.
In addition, a centrifugal pump is not appropriate in the case of a diphasic fluid loop for a space system such as a commercial satellite, since pumps of this type have high electrical consumption, a large size, and a high cost.
Pumps with positive displacement (U.S. Pat. No. 2,797,646, U.S. Pat. No. 4,585,397, U.S. Pat. No. 4,421,464) incorporate many moving parts in dynamic contact (pumps with a reciprocal displacement pumping unit, such as a piston or deformable unit) which are subject to wear, in particular the intake and output valves of the manifold and the parts for transmission of movement to the pumping unit, the service life of which cannot be determined on the ground other than by service life duration tests, which in general are statistical. The performance levels of this type of pump also vary considerably according to the wear, and thus deteriorate over a period of time. In addition, these pumps generate significant stresses on the materials, as well as vibrations and unbalanced forces.
In particular, U.S. Pat. No. 4,421,464 describes a pump pumping liquid helium, comprising bellows which are actuated by an electromagnetic motor, which is totally immersed in the liquid helium. Since the mobile part of the pump and of the motor are connected by flexible electrical connections, and the valves are diaphragm valves, a pump of this type cannot be qualified for space applications with a long service life. In addition, it is not applicable to pumping of fluids such as heat-transfer fluids (for example ammonia) of the diphasic fluid thermal control loops for space systems, with which the components of the motor are not compatible.
Thus, hitherto, it has been considered that pumps with positive displacement cannot be qualified for space applications with a long service life.
In addition, pumping of a thermal control heat-transfer fluid, in particular in a loop with a diphasic fluid, of a space system, requires particularly stringent performance levels, including: a pumping height of several metres, high resistance to static pressure (which can be as much as 160.105 Pa, with permanent deformation, and 80.105 Pa without permanent deformation), a flow rate of several grammes per second, and a reduced energy consumption and size. In addition, it must be possible to vary the power to be transported within an extensive range, and to regulate the flow rate easily (i.e. using an electronic system which is simple, reliable and has a small size).
Thus, the hydrostatic pressure generator described by U.S. Pat. No. 3,657,930, the pumping unit of which consists of a piezoelectric crystal, does not fulfil these criteria, since the amplitude of displacement of a pumping unit of this type is not sufficient. In addition, in this case also, flexible electrical connections must be provided in order to supply the crystal with electrical energy through the wall of the cylinder, thus causing problems of service life. Also, U.S. Pat. No. 3,508,848 describes a single-effect diaphragm pump, with vortex fluid diodes, which is actuated by a pneumatic oscillator. This solution therefore requires a pneumatic external alternative pressure source, to which the aforementioned problems of suitability and service life apply, and which does not make it possible to achieve the above-described performance levels.
In practice therefore, no mechanical pump exists which can be qualified for a long service life, and is designed to be able to be integrated in a space system, and in particular an unmanned commercial satellite or a space station, for pumping of a thermal control heat-transfer fluid, in particular in a diphasic fluid loop.
In particular, even if use of diphasic fluid thermal control loops is theoretically possible in unmanned commercial satellites, practical implementation of these loops is impeded by the fact that there is no corresponding qualified pump.
The object of the invention is thus to eliminate these disadvantages, and to provide a pump with positive displacement which can be integrated in a space system such as a satellite or a space station, and the service life of which in space can be guaranteed on the ground for several years, and in particular for at least ten years.
The object of the invention is also to provide a pump of this type, which more particularly is designed for pumping of a thermal control heat-transfer fluid, and in particular a diphasic heat-transfer fluid of a diphasic fluid loop, for example ammonia.
The object of the invention is also in particular to propose a pump which permits use of diphasic fluid thermal control loops in unmanned commercial satellites or space stations.
The object of the invention is more particularly to propose a pump of this type which has a reduced size and weight, and in particular dimensions of approximately a decimetre for a weight of approximately a kilogramme; the operating characteristics of which remain stable in the long term; which provides a one-way flow, the value of which can easily be piloted, and can be as much as several grammes per second or several cubic centimetres per second, without requiring complex electronic regulation; which provides a pumping height which can be as much as several metres; which can withstand a high static pressure (of up to 160.105 Pa with permanent deformation, and 80.105 Pa without permanent deformation); which has a low energy consumption, and in particular less than 15W; and which has a structure which is simple, robust and inexpensive.
For this purpose, the invention relates to a pump with positive displacement for pumping and entrainment of a fluid in piping, comprising:
at least one cylinder which contains deformable pumping bellows which separate two pumping chambers in this cylinder, one of the pumping chambers being formed inside the bellows, whereas the other is formed outside the bellows, this cylinder being delimited by a wall which is hermetically sealed, with the exception of apertures for intake/output of the fluid, which open into each of the pumping chambers;
drive means which are associated with the bellows, and are designed to deform the latter and displace it reciprocally in the cylinder, the volumes of the two pumping chambers varying in opposition, these drive means comprising at least one ferromagnetic and/or magnetised actuator unit which is disposed inside the cylinder, and is connected to the bellows in order to deform and displace the latter, and coil means, which are disposed outside the wall of the cylinder, for transmission of electromagnetic drive energy by induction to this actuator unit from outside the cylinder, these drive energy transmission means being without a part which passes through the wall of the cylinder, and in particular a mobile part which gives rise to production of dynamic solid friction; and
a manifold with fluid diodes of the vortex type, which is without a mobile unit valve, is connected to the piping and to the intake/output apertures, and is designed to control the global direction of pumping and flow of the fluid in the piping, during reciprocal deformations and displacements of the bellows in the cylinder.
Throughout the text, the following terminology is used:
cylinder: any enclosure which is delimited by a wall (in one or several parts), irrespective of its shape and dimensions;
fluid diode: any device through which a fluid can pass, and which, owing to its shape, has resistance to the flow of the fluid in one direction which is greater than the resistance to the flow of the fluid in the other direction; the fluid diode is said to be xe2x80x9cthrough-puttingxe2x80x9d in the direction in which it offers the least resistance;
dynamic solid friction: contact friction between at least two solids which are in movement relative to one another;
volumes varying in opposition: one volume increases by a value when the other decreases simultaneously by the same value.
Advantageously and according to the invention, the pumping bellows consist of a single deformable piece. These bellows can be made of metal.
In addition, advantageously and according to the invention, the actuator unit is disposed in an extension of the pumping chamber, which is disposed outside the bellows.
The bellows may or may not be symmetrical in revolution around their main axis.
Advantageously and according to the invention, the actuator unit comprises a ferromagnetic and/or magnetised part, which is accommodated in the cylinder, in particular in an extension of one of the two pumping chambers, and which is connected by a rod to an end wall of the pumping bellows, such that this part of the actuator unit and this end wall are integral in translation in the cylinder. The said part, the rod and the end wall of the bellows are accommodated entirely in the cylinder.
In addition, advantageously and according to the invention, the drive means are designed to control the pumping unit at a frequency of between 1 Hz and 50 Hz, and in particular between 1 Hz and 1 Hz.
In addition, advantageously and according to the invention, the pump comprises means for guiding in translation of the actuator unit in the cylinder, consisting of flexible plates, the axial rigidity of which (i.e. according to the axis of expansion and contraction of the bellows) is less than that of the pumping bellows. These means for guiding are also accommodated entirely in the cylinder, are supported on the wall of the cylinder, and are designed not to produce any dynamic solid friction. Since they function solely with axial flexure, they are without any mobile part which would give rise to dynamic solid friction of this type.
Advantageously and according to the invention, interposed between each pumping chamber and a suction end of the piping, the manifold comprises an upstream fluid diode which is through-putting towards the corresponding pumping chamber, and, interposed between each pumping chamber and a delivery end of the piping, a downstream fluid diode, which is through-putting towards the delivery end, such that the pump is of the double-effect type.
According to the invention, the fluid diodes of the manifold are of the vortex type, i.e. they comprise a main cavity which is globally symmetrical in revolution, a first, intake aperture which opens axially into the cavity, and a second, output aperture, which opens tangentially into the cavity.
Since the vortex fluid diodes do not have any solid/solid dynamic contact, they are without a mobile part and deformable portions. They are therefore entirely, perfectly static.
In addition, advantageously and according to the invention, the manifold comprises an upstream accumulator cavity, which receives the fluid from the suction end of the piping, and a downstream accumulator cavity, from which the fluid is delivered towards the delivery end of the piping, and the fluid diodes are interposed between the accumulator cavities and the intake/output apertures in the pumping chambers. These accumulator cavities make it possible to compensate for any instantaneous variations in the global flow rate in the piping.
The invention additionally relates to a device for thermal control of the components of a space system, such as a satellite or a space station, comprising a diphasic heat-transfer fluid loop, and at least one pump according to the invention.
The pump according to the invention is entirely without any mobile part which is in solid/solid contact, or which undergoes dynamic solid friction. Thus, its service life can easily be determined on the ground, in particular by means of accelerated tests, and this service life is substantial, and in particular approximately several years.
In addition, the pump according to the invention is advantageously a double-effect bellows pump, which provides a relatively regular flow rate, and little vibration, in which the bellows are subjected to balanced pressure stresses on both sides of the deformable pumping unit, and have low energy consumption. Their characteristics remain constant in the long term.
A pump according to the invention can easily be produced in a form which is suitable for integration of the pump in a space system such as an unmanned commercial satellite. It is extremely simple, has a small size, and is inexpensive. It has high performance levels which are compatible with those of thermal control devices such as the diphasic fluid loops of the space systems.
A pump according to the invention is thus particularly well-suited for pumping the fluid of a diphasic heat-transfer fluid of a thermal control loop. In particular, its flow rate can easily be piloted, for example by adjusting the operating frequency of the bellows. In addition, the real flow rate which is delivered by the pump varies little according to the variations of losses of load in the piping.
The invention also extends to a pump and a thermal control device, characterised in combination by all or some of the characteristics described previously or hereinafter.